I suspect that people have a negative perception of Southwest Airlines for one or more of the following reasons:
1. The low-fare reputation carries a stigma that rubs off on the customers ("Can't they afford to fly a REAL airline?") People who see their airline choice as a fashion statement will avoid Southwest.
2. They have flown Southwest only to or from Las Vegas or Orlando, on flights packed with leisure travelers. Those flights might as well be on a different airline than the typical Southwest flight, which carries mostly business travelers.
3. They blame Southwest for the demise legacy airlines, confusing the effects of deregulation with their cause. The more successful Southwest becomes, the more these people resent it.
4. They have watched A&E's Airline, a "reality" show that bore almost no relationship with reality. Anyone who believes that Airline protrayed anything you will ever see on Southwest is mistaken. We FTers haven't seen any of those antics on Southwest in our many thousands of flights.
Southwest provides reasonably priced reliable coach transportation, coupled with a frequent flier program that works well only for short-haul travelers. Their web site rocks, and they answer the phone quickly with a real live native English speaking person. Maybe this package fits your needs, and maybe it doesn't. But if you are getting too much attitude at altitude, I don't think you will find better front-line employees anywhere.